- 标题
- 摘要
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- 实验方案
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Selective oxidation of the surface layer of bilayer WSe <sub/>2</sub> by laser heating
摘要： WSe2 films have several anisotropies between the in-plane and out-of-plane directions, which affects their responses to external operation. Guided by the anisotropies, we provide adequate heat propagation to oxidize selectively the surface layer of bilayer WSe2 and characterized the structure of monolayer WSe2 covered with an oxidized layer by optical and atomic force microscopy, Raman spectroscopy and photoluminescence measurements. Furthermore, we found indications that laser treatments of monolayer WSe2 covered with an oxidized layer have possibility to cause photoactivated oxidation. Our observations suggest clues to understand low-dimensional oxidation behaviours.
关键词： anisotropy,laser heating,WSe2,selective oxidation,photoluminescence
更新于2025-09-12 10:27:22
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Phase-transition modulated, high-performance dual-mode photodetectors based on WSe <sub/>2</sub> /VO <sub/>2</sub> heterojunctions
摘要： Photodetectors based on two-dimensional (2D) transition metal dichalcogenides (TMDs) can only be operated in a single photovoltaic or photoconductive mode, showing either high detectivity or high responsivity, but not both. An effort to develop a photodetector that can dynamically switch its working mode is indispensable for practical applications. In this article, we demonstrate a high performance, phase-transition modulated, dual-mode photodetector based on WSe2/VO2 heterojunction. Enabled by the insulator-to-metal transition of VO2, the WSe2/VO2 heterojunction can be regulated from a type-II heterojunction to a Schottky junction, showing a tunable built-in electric field at the heterojunction interface. This resulted in the dynamic switch of carrier transport and photoresponse in the heterojunction. With this dual-mode function, the new photodetector can have both a high detectivity and a large responsivity, surpassing the current performance of single mode 2D TMDs photodetectors. With a direct laser writing and erasing technique, the photoresponse of a WSe2/VO2 device can be locally modulated as desired. This dual mode detection of the WSe2/VO2 photodetector deepens the fundamental understanding of charge transfer in heterojunctions and favors versatile applications in photodetection.
关键词： Photodetectors,Phase-transition,2D materials,WSe2/VO2 heterojunction,Dual-mode
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - MoSe <sub/>2</sub> and WSe <sub/>2</sub> Embedded in Bragg-Cavities with High Q-Factors Enabling Strong Exciton-Polariton Coupling in 2D-Systems
摘要： Transition metal dichalcogenides (TMDCs) are semiconducting 2D-materials with a direct bandgap in a range of 1.0 to 2.5 eV. The electronic and optical properties of TMDCs are dominated by strongly bound excitons, suitable for the observation of coupled light-matter interactions in highly resonant cavities. From an application point of view, such cavities must not only provide high Q-factors but must also be robust and reproducible. We report on the fabrication of TMDC-loaded cavities, carried out in an ion-assisted deposition (IAD) process. Mechanically exfoliated MoSe2 and WSe2 monolayer flakes were placed on a sputtered DBR made of SiO2 and TiO2 layers. The second cavity mirror consisting of eight SiO2-TiO2-pairs was deposited directly on the top via IAD, preserving gentle coating conditions to comply with the weak van-der-Waals adhesion of the TMDC flakes. A top-view of a TMDC-loaded part before and after the coating process of the cavity is depicted in Fig. 1(a). Experimental PL measurements with multiple cooling-heating cycles between 5 K and 300 K (shown in Fig. 1(b)), indicate that the process does not damage the TMDC-flakes. A resonance bandwidth of (cid:543)(cid:2019) = 0.16 nm was determined for the cavity, equating into a Q-factor of (cid:1869) = 4683. With PL measurements on a FIB-cut lamella, the presence of pristine, high-quality MoSe2 in the cavity was proven [5]. Further PL measurements showed that the excitons do strongly couple to the cavity mode, verified with Zeeman-splitting of the hybridized polaritonic branches (shown in Fig. 1(c)). The influence of a magnetic field splits and polarizes the hybrid light-matter coupled groundstate, which indicates a polaritonic resonance. The fit to a coupled oscillator model showed a Rabi splitting of about 51 meV and a detuning of about 55 meV corresponding to a |(cid:1850)(cid:2870)|~ 0.13. Based on our findings, we will discuss concrete technical steps, to increase of the optical Q-factor and enhance the exciton linewidth, which will lead to room-temperature strong coupling.
关键词： high Q-factors,exciton-polariton coupling,2D-systems,MoSe2,WSe2,Bragg-Cavities
更新于2025-09-12 10:27:22
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Toward Coupling Color Centers in Single Crystal Diamond to Two-Dimensional Materials
摘要： Individual nitrogen vacancy (NV) color centers in diamond are bright, photo-stable, atomic-sized dipole emitters [1]. Consequently, they represent optimal candidates for novel scanning near field microscopy techniques [2]. Here, NV centers form one member of a F¨orster Resonance Energy Transfer (FRET) pair. Due to their broadband emission (> 100 nm), NVs are versatile donors for FRET to systems absorbing in the near infrared spectral range. Highly-promising applications include, e.g., nanoscale imaging of fluorescent molecules or nanomaterials like graphene [2]. Critical parameters for FRET are the NV’s quantum efficiency, charge state stability and NV-sample-distance. Previous experiments used NVs in nanodiamond for FRET [2], however these NVs might suffer from quenching, instability and badly controlled surface termination. We here address this issue by using shallowly implanted NV centers in optimized cylindrical nanostructures [3] used as scanning probes in our homebuilt combination of a confocal and an atomic force microscope. In recent years, two-dimensional materials especially monolayers of semiconducting materials are of major interest in research. Particularly, dichalcogenides like, e.g., tungsten diselenide (WSe2) are promising candidates for a varity of applications [4]. WSe2 emits photons at a wavelength of around 750 nm while absorbing photons below 700 nm [4] which renders WSe2 as a promising FRET partner for NV centers. Here, we present first results towards demonstrating the interaction of NV color centers in single crystal diamond with WSe2. We envisage using quenching of the NV center sued as a donor in FRET in close proximity to the 2D material as a valuable sensing ressource.
关键词： F¨orster Resonance Energy Transfer (FRET),tungsten diselenide (WSe2),nitrogen vacancy (NV) color centers,diamond,two-dimensional materials
更新于2025-09-11 14:15:04
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Quantum Multibody Interactions in Halide-Assisted Vapor-Synthesized Monolayer WSe <sub/>2</sub> and Its Integration in a High Responsivity Photodetector with Low-Interface Trap Density
摘要： Among the two-dimensional (2D) transitional-metal dichalcogenides, monolayer (1L) tungsten diselenide (WSe2) has recently attracted a great deal of interest because of its direct band gap and tunable charge transport behavior, making it attractive for a variety of electronic and optoelectronic applications. Controlled and efficient synthesis of 1L WSe2 using chemical vapor deposition (CVD) is often challenging because of the high temperatures required to generate a steady flux of tungsten atoms in the vapor phase from the oxide precursors. Here, the use of halide-assisted low-pressure CVD with NaCl helps to reduce the growth temperature to ～750 °C, which is lower than the typical temperatures needed with conventional CVD for realizing 1L WSe2. Moreover, we experimentally probed the quantum multibody interactions in 1L WSe2 ascribed to excitons, trions, and other localized states by analyzing the temperature-dependent photoluminescence spectra, where such multibody interactions govern the intrinsic electronic and optoelectronic properties of 1L WSe2 for device platforms. The role of the metal?2D semiconductor interface is also critical to realize high-performance devices. In this study, a 1L WSe2-based photodetector was fabricated using Al contacts, which shows a high photoresponsivity, and the interface-state density Dit of the Al/WSe2 junction was computed to be the lowest reported to date ～3.45 × 1012 cm?2 eV?1. Our work demonstrates the tremendous potential of WSe2 to open avenues for state-of-the-art electronic, optoelectronic, and quantum-optoelectronic devices using scalable synthesis routes.
关键词： transitional-metal dichalcogenides,photodetector,tungsten diselenide (WSe2),two-dimensional (2D) materials,quantum multibody interactions,interface-state density,chemical vapor deposition (CVD)
更新于2025-09-11 14:15:04
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Ambipolar and Robust WSe <sub/>2</sub> Field‐Effect Transistors Utilizing Self‐Assembled Edge Oxides
摘要： Transition metal oxides (TMOs) with high work function (WF) show promising properties as unipolar p-type contacts for transition metal dichalcogenides. Here, ambipolar field-effect transistors (FETs) enabled by bilayer WSe2 with self-assembled TMOs (WO2.57) as contacts are reported. Systematic material characterizations demonstrate the formation of WO2.57/WSe2 heterojunctions around nanoflake edges with Se atoms substituted by O atoms after air-exposure, while pristine properties of WSe2 almost sustain in inner domains. As-fabricated FETs exhibit both polarities, implying WO2.57 with lowered WF at edges can serve as both the p-type and n-type contact for inner WSe2. Noteworthy, greatly reduced contact resistance and enhanced channel current are achieved, compared to the devices without WO2.57 contacts. Linear drain–source current relationship from 77 to 300 K indicates the ohmic contact between edge WO2.57 and inner WSe2. Density functional theory calculations further reveal that the WO2.57/WSe2 heterojunction forms a barrier-less charge distribution. These nm-scale FETs possess remarkable electrical conductivity up to ≈2600 S m?1, ultra-low leakage current down to ≈10?12 A, robustness for high voltage operation, and air stability, which even outperform pristine WSe2 FETs. Theoretical calculations reveal that the high conductivity is exclusively attributed to the air-induced WO2.57 and its further carrier injection to WSe2.
关键词： field-effect transistors,self-passivation,WOx,density functional theory,WSe2
更新于2025-09-11 14:15:04
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Photodetector based on heterostructure of two-dimensional WSe2/In2Se3
摘要： Heterojunctions formed by two-dimensional (2D) layered semiconducting materials have been studied extensively in the past several years. These van der Waals (vdW) structures have shown great potential in future electronic and optoelectronic devices. However, the optoelectronic performance of these devices is limited by the indirect band gap of the multilayer materials and low light absorption of single layer materials. Here, we fabricate photodetectors based on heterojunctions composed of n-type multilayer α-Indium Selenide (In2Se3) and p-type Tungsten Diselenide (WSe2) for the first time. The direct band gap of multilayer α-In2Se3 and type-II band alignment of the WSe2/In2Se3 heterojunction enable high optoelectronic performance of the devices at room temperature in the air. Without light illumination, the dark current is effectively suppressed to 10-13 A under -1 V bias and a high rectification ratio of 7.37×103 is observed. Upon laser illumination with the wavelength of 650 nm, the typical heterojunction device exhibits a photocurrent on/off ratio exceeding 1.24×105, a maximum photo responsivity of 26 mA/W and short photoresponse time of 2.22 ms. Moreover, the heterojunction photodetectors show obvious light response in the wavelength range from 650 nm to 900 nm. The present 2D vdW heterojunctions composed of direct band gap multilayer materials show great potential in future optoelectronic devices.
关键词： In2Se3,photodetector,two-dimensional materials,WSe2,direct band gap materials,heterojunction
更新于2025-09-11 14:15:04
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Dark exciton brightening and its engaged valley dynamics in monolayer
摘要： We theoretically investigate the valley Zeeman splitting, dark-exciton brightening, and magnetic-field-controlled dark-exciton engaged valley dynamics in monolayer WSe2 subjected to a tilted magnetic field B. In Faraday geometry (out-of-plane B⊥), only bright-exciton emissions emerge, and the valley polarization (VP) as a function of B⊥ for σ + and σ ? circularly polarized laser excitations features an “X” pattern, i.e., the VP is locked to the valley. We also find that the photoluminescence (PL) intensity exhibits a similar behavior to VP. In the Voigt geometry (in-plane B(cid:3)), however, aside from the bright-exciton emission, the dark exciton becomes brightening. The PL intensity of the dark exciton is enhanced parabolically with increasing B(cid:3), independent of the pumping laser helicity. For B along any other direction, as B increases, the dark-exciton emission intensity increases but depends on the pumping laser helicity, accompanied by an decrease of its VP. Furthermore, not only the bright-exciton but also the dark-exciton emission peak splits for laser excitation with different circular polarizations. In addition, the latter demonstrates a much larger peak splitting than the former, which facilitates individual manipulation of each of the two valleys. Our theory paves the way for a study of the properties of bright-dark hybrid states with lifetime orders of magnitude longer than that of the bright states, which is desirable for fields of either spintronics or valleytronics (or their combination).
关键词： monolayer WSe2,dark-exciton brightening,tilted magnetic field,valley dynamics,valley Zeeman splitting
更新于2025-09-11 14:15:04
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Suppressing Ambipolar Characteristics of WSe <sub/>2</sub> Field Effect Transistors Using Graphene Oxide
摘要： Monolayer (1L) tungsten diselenide (WSe2) is of interest for next generation ultrathin flexible electronic devices. However, typical WSe2 field effect transistors (FETs) show ambipolar characteristics that are not desirable for complementary field-effect-transistors and circuits. Here, significant suppression of the ambipolar characteristics of a 1L-WSe2 FET is demonstrated by using an electron withdrawing functional group of graphene oxide (GO). The pristine 1L-WSe2 FET shows n-type dominant ambipolar characteristics, whereas the GO coated 1L-WSe2 FET shows unipolar p-type behavior with a huge decrease (1/106) of current level of the n-channel. Also, the current level of the p-channel increases up to ten times that of the pristine 1L-WSe2 FET. These results are applicable for the realization of flexible nanoscale digital logic devices by using transition metal dichalcogenides.
关键词： field-effect-transistors,ambipolar,monolayer WSe2,unipolar,electron-withdrawing group
更新于2025-09-10 09:29:36
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Impact of Post-Lithography Polymer Residue on the Electrical Characteristics of MoS <sub/>2</sub> and WSe <sub/>2</sub> Field Effect Transistors
摘要： The residue of common photo- and electron-beam resists, such as poly(methyl methacrylate) (PMMA), is often present on the surface of 2D crystals after device fabrication. The residue degrades device properties by decreasing carrier mobility and creating unwanted doping. Here, MoS2 and WSe2 field effect transistors (FETs) with residue are cleaned by contact mode atomic force microscopy (AFM) and the impact of the residue on: 1) the intrinsic electrical properties, and 2) the effectiveness of electric double layer (EDL) gating are measured. After cleaning, AFM measurements confirm that the surface roughness decreases to its intrinsic state (i.e., ≈0.23 nm for exfoliated MoS2 and WSe2) and Raman spectroscopy shows that the characteristic peak intensities (E2g and A1g) increase. PMMA residue causes p-type doping corresponding to a charge density of ≈7 × 1011 cm?2 on back-gated MoS2 and WSe2 FETs. For FETs gated with polyethylene oxide (PEO)76:CsClO4, removing the residue increases the charge density by 4.5 × 1012 cm?2, and the maximum drain current by 247% (statistically significant, p < 0.05). Removing the residue likely allows the ions to be positioned closer to the channel surface, which is essential for achieving the best possible electrostatic gate control in ion-gated devices.
关键词： MoS2,ionic gating,WSe2,field effect transistor,polymer residue
更新于2025-09-10 09:29:36